# CHOSEN COVID-19 score (Levine)

CHOSEN

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/chosen`
HTML: https://magentlab.com/docs/chosen
Markdown: https://magentlab.com/docs/chosen.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Sum the Levine 2020 CHOSEN (COVID Home Safely Now) Figure 2 points from age, oxygen saturation, and serum albumin in g/dL, and return whether the total is at or above the printed cutpoint of 30.

## When to use

When an agent already has adult age, SpO2, and albumin in g/dL and needs the published three-item CHOSEN total (0–55) and the ≥30 cutpoint flag, not a discharge order and not a competing model that adds sex or respiratory rate.

## When not to use

- Not a medical device.
- Not a discharge order. magent does not decide disposition, prescribe oxygen, or examine the patient.
- The derivation outcome is a 14-day composite of hypoxia (need for supplemental oxygen), ICU admission, and death in March–April 2020 Mass General Brigham adults with COVID-19. A higher score favored event-free status in that cohort.
- Figure 2 is the three-item model (age, SpO2, albumin g/dL). Sex and respiratory rate are not scored here.
- Cutpoint 30 is the printed derivation threshold (sensitivity 83%, specificity 82%). magent does not convert the total into an individual probability.

## Formula

```
CHOSEN = age_points + spo2_points + albumin_points; Levine 2020 Figure 2; age 18-45 → 5, 46-59 → 2, 60-73 → 1, >73 → 0; SpO2 % <94 → 0, 94-96 → 9, 97-98 → 14, >98 → 21; albumin g/dL <2.8 → 0, 2.8-3.3 → 5, 3.4-3.7 → 15, >3.7 → 29; range 0-55; at_or_above_cutpoint iff score ≥30 (derivation sensitivity 83%, specificity 82%)
```

## Citation

[Derivation of a clinical risk score to predict 14-day occurrence of hypoxia, ICU admission, and death among patients with coronavirus disease 2019](https://doi.org/10.1007/s11606-020-06353-5)
Levine DM, Lipsitz SR, Co Z, Song W, Dykes PC, Samal L
J Gen Intern Med. 2021;36(3):730-737
DOI: [10.1007/s11606-020-06353-5](https://doi.org/10.1007/s11606-020-06353-5)

## Worked example

### Age 40, SpO2 99, albumin 4.0 g/dL (score 55)

Given: `age=40, albumin_g_dl=4.0, spo2_percent=99`

1. Age 40 (18-45) → 5
2. SpO2 99 (>98) → 21
3. Albumin 4.0 g/dL (>3.7) → 29
4. Score = 55 (max 55); at_or_above_cutpoint = true


### Age >73, SpO2 <94, albumin <2.8 (score 0)

Given: `age=80, albumin_g_dl=2.5, spo2_percent=90`

1. Age 80 (>73) → 0
2. SpO2 90 (<94) → 0
3. Albumin 2.5 g/dL (<2.8) → 0
4. Score = 0 (max 55); at_or_above_cutpoint = false


### Cutpoint neighborhood: score 29

Given: `age=40, albumin_g_dl=3.5, spo2_percent=95`

1. Age 40 → 5; SpO2 95 (94-96) → 9; albumin 3.5 (3.4-3.7) → 15
2. Score = 29; at_or_above_cutpoint = false


### Cutpoint neighborhood: score 30

Given: `age=65, albumin_g_dl=3.5, spo2_percent=97`

1. Age 65 (60-73) → 1; SpO2 97 (97-98) → 14; albumin 3.5 (3.4-3.7) → 15
2. Score = 30; at_or_above_cutpoint = true


## Also searched as

- CHOSEN
- COVID Home Safely Now
- Levine CHOSEN
- CHOSEN risk score
- COVID-19 discharge score
- Levine 2020 COVID score
- albumin oxygen saturation age COVID

## Parameters

- `age` (integer, required): Age in years (integer 18-120). Levine 2020 Figure 2: 18-45 → 5; 46-59 → 2; 60-73 → 1; >73 → 0. Age 73 scores 1; age 74 scores 0. Adults as in the derivation cohort.
- `spo2_percent` (number, required): Oxygen saturation percent (50-100). Levine 2020 Figure 2: <94 → 0; 94-96 → 9; 97-98 → 14; >98 → 21. magent does not measure SpO2.
- `albumin_g_dl` (number, required): Serum albumin in g/dL (1.0-6.0). Levine 2020 Figure 2: <2.8 → 0; 2.8-3.3 → 5; 3.4-3.7 → 15; >3.7 → 29. Not g/L. magent does not assay albumin.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/chosen`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "age": "40",
      "albumin_g_dl": "4.0",
      "spo2_percent": "99"
    },
    {
      "age": "40",
      "albumin_g_dl": "4.0",
      "spo2_percent": "99"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/chosen

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/chosen",
  "items": [
    {
      "components": [
        {
          "value": 40,
          "factor": "age",
          "points": 5,
          "present": true
        },
        {
          "value": 99.0,
          "factor": "spo2_percent",
          "points": 21,
          "present": true
        },
        {
          "value": 4.0,
          "factor": "albumin_g_dl",
          "points": 29,
          "present": true
        }
      ],
      "age": 40,
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Levine DM, Lipsitz SR, Co Z, Song W, Dykes PC, Samal L",
        "doi": "10.1007/s11606-020-06353-5",
        "id": "levine-2020-chosen",
        "pmid": "33274414",
        "source": "J Gen Intern Med. 2021;36(3):730-737",
        "title": "Derivation of a clinical risk score to predict 14-day occurrence of hypoxia, ICU admission, and death among patients with coronavirus disease 2019"
      },
      "formula": "chosen",
      "formula_expression": "CHOSEN = age_points + spo2_points + albumin_points; Levine 2020 Figure 2; age 18-45 → 5, 46-59 → 2, 60-73 → 1, >73 → 0; SpO2 % <94 → 0, 94-96 → 9, 97-98 → 14, >98 → 21; albumin g/dL <2.8 → 0, 2.8-3.3 → 5, 3.4-3.7 → 15, >3.7 → 29; range 0-55; at_or_above_cutpoint iff score ≥30 (derivation sensitivity 83%, specificity 82%)",
      "max_score": 55,
      "score": 55,
      "albumin_g_dl": 4.0,
      "spo2_percent": 99.0,
      "at_or_above_cutpoint": true,
      "cutpoint": 30
    },
    {
      "components": [
        {
          "value": 40,
          "factor": "age",
          "points": 5,
          "present": true
        },
        {
          "value": 99.0,
          "factor": "spo2_percent",
          "points": 21,
          "present": true
        },
        {
          "value": 4.0,
          "factor": "albumin_g_dl",
          "points": 29,
          "present": true
        }
      ],
      "age": 40,
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Levine DM, Lipsitz SR, Co Z, Song W, Dykes PC, Samal L",
        "doi": "10.1007/s11606-020-06353-5",
        "id": "levine-2020-chosen",
        "pmid": "33274414",
        "source": "J Gen Intern Med. 2021;36(3):730-737",
        "title": "Derivation of a clinical risk score to predict 14-day occurrence of hypoxia, ICU admission, and death among patients with coronavirus disease 2019"
      },
      "formula": "chosen",
      "formula_expression": "CHOSEN = age_points + spo2_points + albumin_points; Levine 2020 Figure 2; age 18-45 → 5, 46-59 → 2, 60-73 → 1, >73 → 0; SpO2 % <94 → 0, 94-96 → 9, 97-98 → 14, >98 → 21; albumin g/dL <2.8 → 0, 2.8-3.3 → 5, 3.4-3.7 → 15, >3.7 → 29; range 0-55; at_or_above_cutpoint iff score ≥30 (derivation sensitivity 83%, specificity 82%)",
      "max_score": 55,
      "score": 55,
      "albumin_g_dl": 4.0,
      "spo2_percent": 99.0,
      "at_or_above_cutpoint": true,
      "cutpoint": 30
    }
  ]
}
```

## Response fields

- `formula` (string): chosen
- `formula_expression` (string): Exact expression used
- `score` (integer): CHOSEN points 0-55
- `max_score` (integer): Always 55 (5+21+29)
- `cutpoint` (integer): Levine 2020 printed cutpoint 30
- `at_or_above_cutpoint` (boolean): true iff score ≥30 (Levine 2020 derivation sensitivity 83%, specificity 82%). Not a discharge order.
- `age` (integer): Age used, years
- `spo2_percent` (number): Oxygen saturation percent used
- `albumin_g_dl` (number): Serum albumin in g/dL used
- `components` (array): Per-predictor points
- `citation` (object): Levine 2020 JGIM citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "components": [
    {
      "value": 40,
      "factor": "age",
      "points": 5,
      "present": true
    },
    {
      "value": 99.0,
      "factor": "spo2_percent",
      "points": 21,
      "present": true
    },
    {
      "value": 4.0,
      "factor": "albumin_g_dl",
      "points": 29,
      "present": true
    }
  ],
  "age": 40,
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Levine DM, Lipsitz SR, Co Z, Song W, Dykes PC, Samal L",
    "doi": "10.1007/s11606-020-06353-5",
    "id": "levine-2020-chosen",
    "pmid": "33274414",
    "source": "J Gen Intern Med. 2021;36(3):730-737",
    "title": "Derivation of a clinical risk score to predict 14-day occurrence of hypoxia, ICU admission, and death among patients with coronavirus disease 2019"
  },
  "formula": "chosen",
  "formula_expression": "CHOSEN = age_points + spo2_points + albumin_points; Levine 2020 Figure 2; age 18-45 → 5, 46-59 → 2, 60-73 → 1, >73 → 0; SpO2 % <94 → 0, 94-96 → 9, 97-98 → 14, >98 → 21; albumin g/dL <2.8 → 0, 2.8-3.3 → 5, 3.4-3.7 → 15, >3.7 → 29; range 0-55; at_or_above_cutpoint iff score ≥30 (derivation sensitivity 83%, specificity 82%)",
  "max_score": 55,
  "score": 55,
  "albumin_g_dl": 4.0,
  "spo2_percent": 99.0,
  "at_or_above_cutpoint": true,
  "cutpoint": 30
}
```

## Errors

- HTTP 400 `invalid_chosen`: CHOSEN inputs must match Levine 2020 age, oxygen saturation, and albumin bands. Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [4C](https://magentlab.com/docs/4c) — Sum the Knight 2020 ISARIC 4C Mortality Score items and return the published Table 5 band (low, intermediate, high, or very high).
- [PRIEST](https://magentlab.com/docs/priest) — Sum the Goodacre 2021 PRIEST points from NEWS2 Chart 1 Scale 1 vitals, alertness, inspired oxygen, age, sex, and performance status, and return whether the total is ≤4.
- [BCRSS](https://magentlab.com/docs/brescia-covid) — Count the four Duca 2020 BCRSS testing-criteria binaries as assigned by the caller and return the integer total (0–4).

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.